Transmission Electron Microscopy Investigation Of TiO₂Nanomaterials And The Synthetic Product Na₃TiOF₅

Titanium dioxide (TiO2) is a wide-band-gap semiconductor metal oxide, the band gaps of rutile and anatase are3.03eV and3.20eV respectively. Usually in the nature, the common phase of TiO2are rutile, anatase and brookite. Rutile phase is the most stable TiO2phase, and anatase phase is the most effective and widely used in the field of catalyst, photochemical and electrochemical fields. Anatase phase within the temperature range from700to1000degrees Celsius, will be transformed into rutile phase and rutile phase after the temperature cooling won’t shift back to anatase phase. Catalytic activity is usually associated with the surface of the material, especially highly active surface. But highly active surface in the process of crystal growth typically fast disappear to lower the overall surface energy. For TiO2anatase phase, the most available TiO2anatase phase is mainly composed of thermodynamic stability of{101} surface not higher activity of {001} plane. So long synthesis of the stable inorganic single crystal with the highly reactive surface has been extensive studied. In2008it is firstly reported using hydrofluoric acid as surface morphology control agent successful synthesis of high surface area with highly active{001} plane anatase TiO2single crystal. In dye-sensitised cells, nanometer anatase TiO2particles consisting of porous membrane is the core of the battery, when the sunlight reaching adsorption of dye molecules on nanometer, TiO2particles absorb light produce photoelectrons, electrons conduct easily through the TiO2particles on the transparent conductive film. In this paper, by using transmission electron microscopy the highly active {001} plane anatase TiO2nanosheets with high {001} surface area, the inorganic oxyfluoride Na3TiOF5which is the intermediate product in the process of synthesis anatase TiO2nanosheets and anatase TiO2nanoparticles are studied, the thesis mainly divided into three parts:The first part is about micro structure characterization of the high surface area and highly active {001} plane anatase TiO2nanosheets and structure analysis of the intermediate Na3TiOF5phase. Microstructure characterization found TiO2anatase nanosheet is composed of the eight surface shape which contain the activity of two flat {001} planes and the other eight isosceles trapezoid{101} planes. The nanosheet thickness is roughly around10nm. Found in the product at the same time the micron of tablet sample, through the three-dimensional reciprocal lattice reconstruction and energy spectrum analysis, it is determined that the intermediate phase is the monoclinic inorganic oxyfluoride Na3TiOF5.The second part is about the electron microscopy analysis of domain structure of intermediate Na3TiOF5and the research of space group theory. In electron diffraction experiment, it is found that much of the results is made up of two sets of electron diffraction pattern, through a series tilted selected area electron diffraction of samples, found that the pattern between some fixed orientation relationship formed by the domain structure. We know that in the process of phase transition is accompanied by the reduction of some symmetry, in low symmetry phase will often find domain structure. Reports indicate that Na3TiOF5will transform from cubic phase to monoclinic phase when the temperature change from873k down to room temperature. Through a detailed group theory analysis, the orientation domains are shown to exhibit12variants and11domain boundaries, which can be categorized into three types of perpendicular twins and two types of antiparallel twins. The result deduced by group theoy elucidate the experimental observations.The third part is mainly about the high-resolution electron microscopy studying of the interface of anatase TiO2nanoparticles growed by orientied attachment. Attachment typically happened on{101},{112} and{001} planes. Material growed by orientied attachment can form single crystals or twinning structure. Through the HRTEM studying we found that the burgers vector of the dislocation is1/2<101>.